Magnetic recording medium and production method thereof

ABSTRACT

A magnetic recording medium comprising a smooth recording layer constituted of magnetic particles having a small size, which has a high coercive force. The magnetic recording medium comprises a substrate body, a Cr undercoat with an oxygen content of 100 wt ppm or less, and ferromagnetic metal made of CoCrTa having an oxygen content of 100 wt ppm or less, and which utilizes magnetic inversion. The ferromagnetic metal layer comprises 14 to 23 atm % chromium(Cr), 2 to 8 atom % tantalum(Ta) and the balance of cobalt(Co).

TECHNOLOGICAL FIELD

The present invention relates to a magnetic recording medium and to aproduction method thereof. In greater detail, the present inventionrelates to a magnetic recording medium and a production method thereofwhich is capable of achieving a high recording density irrespective ofthe electrical properties of the substrate body.

BACKGROUND ART

Conventionally, the following technologies are known for magneticrecording media.

(1) In international application PCT/JP94/01184, it is disclosed that ina magnetic recording medium formed by means of a sputtering formationmethod in an ultraclean atmosphere (having an attained vacuum degree of10⁻⁹ Torr or less), it is possible to limit the amount of oxygencontained in the undercoat and the magnetic layer comprising themagnetic recording medium to 100 wt.ppm or less, and because it ispossible to limit the exchange interaction of the crystalline particlescomprising the magnetic layer, the magnetic characteristics (thecoercive force, and the normalized coercive force) and the storage andreadout characteristics (S/N) are improved.

(2) It is well known that when ferromagnetic metal layers are laminated,by applying an electrical bias to the substrate body, the magneticcharacteristics are improved. In particular, it has been reported byOkumura et al. that when the ferromagnetic metal layer comprises analloy film consisting of CoCrTa, this effect is dramatic ("Substratebias effect on the magnetization of a Co alloy/Cr thin film," Nippon OyoJiki Gakkai Gaiyoushu (1991), 413, p 413, 1991).

(3) It has been made clear by Iwabune et al. that in order to achieve anincrease in the recording density of magnetic recording media, amagnetic recording medium having a small surface roughness is optimal("Dependence of reproduction output on spacing in vertical two layermedia", Nippon Oyo Jiki Gakkaishi, Volume 16, p. 105, 1992). That is tosay, the small surface roughness of the magnetic recording mediumrealizes a lessening of the distance at which the head floats. As aresult, the reproduced signal increases, so that this indicates that itwould be possible to conduct readout of smaller recording bits.

(4) It is commonly known that in order to achieve an increase in therecording density of magnetic recording media, it is necessary to reducemedium noise (Nm). That is to say, it is important to increase the S/Nmratio (reproduction signal (S)), and in order to accomplish this, it isnecessary to reduce the magnetization transition region produced betweenadjacent storage bits. A method in which the recording layer is formedfrom magnetic particles having a small diameter has been disclosed byNakai et al. as a way of accomplishing this ("Effect of Microstructureon Media Noise of CoCrTa Thin Film Media Fabricated under UltraCleanSputtering Process", 1995 IEEE International Magnetics ConferenceDigests of the Technical Papers, JA-05, 1995).

However, when the technique described in (2) above is employed, thesurface roughness of the magnetic recording medium is large, and thereis a tendency for the diameter of the magnetic particles to becomedisarranged and chaotic. This tendency is identical when the techniquedescribed in (1) above is employed. As a result, it is difficult toproduce a magnetic recording medium having a small head float distanceand having low medium noise.

Accordingly, the development of a magnetic recording medium, and amanufacturing method thereof, having a small surface roughness andhaving a recording layer which is formed from magnetic particles havinga small diameter, is desirable from the point of view of furthering anincrease in the recording density of magnetic recording media.

The present invention has as an object thereof to provide a magneticrecording medium and a manufacturing method thereof, comprising arecording layer comprising magnetic particles having a small diameterand having a small surface roughness, and having a high coercive force.

DISCLOSURE OF THE INVENTION

The magnetic recording medium of the present invention comprises aferromagnetic metal layer comprising CoCrTa having an oxygenconcentration of 100 wt.ppm or less provided on a substrate body via ametallic undercoat, wherein the composition of said ferromagnetic metallayer contains 14-23 atm % of chromium (Cr), 2-8 atm % of tantalum (Ta)and the balance of cobalt (Co).

When a magnetic recording medium is formed by providing a ferromagneticmetal layer comprising CoCrTa having an oxygen content of 100 wt.ppm orless via a metallic undercoat on a substrate body layer, by means offormation in an ultraclean atmosphere, by setting the composition of theferromagnetic metal layer so as to comprise 14-23 atm % chromium (Cr),2-8 atm % tantalum (Ta), and the balance of cobalt (Co), it is possibleto effectively segregate the Cr to the intergranular boundary, and toform a nonmagnetic granular boundary layer, and it is thus possible toobtain a ferromagnetic metal layer comprising magnetic particles havinga high degree of magnetic isolation without applying a substrate bias.As a result, it is possible to promote the segregation of the Cr to theintergranular boundary without greatly reducing the saturationmagnetization and anisotropic magnetic field of the ferromagnetic metallayer, so that it is possible to obtain a magnetic recording mediumhaving low noise which is optimal for an increase in recording density.

In particular, when the amount of Cr contained is within a range of14-23 atm %, it is possible to provide a coercive force of 2000 Oe ormore, and to reduce the medium noise Nm to less than one half that inthe case of a conventional CoCrTa medium (where Cr: 10.5 atm %, Ta: 4atm %, the remainder being Co). Ta is added in order to promote thesegregation of the Cr; the minimum amount of Ta at which this phenomenoncan be observed has been experimentally determined to be 2 atm %.Furthermore, when Ta is present at a level of more than 8 atm %, thestructure of the magnetic layer changes greatly, becoming locallyamorphous, and as a result, the coercive force drops precipitously.Accordingly, the optimal amount of Ta contained is within a range of 2-8atm %.

Furthermore, when at least a ferromagnetic metal layer is produced, amagnetic recording medium having a small surface roughness appropriatefor an increase in recording density can be obtained by means of amanufacturing method for magnetic recording medium in which anelectrical bias is not applied to the substrate body at least during theproduction of the ferromagnetic metal layer.

Hereinbelow, embodied modes of the present invention will be explainedwith reference to the figures.

Substrate Body

Examples of the substrate body in the present invention include, forexample, aluminum, titanium, and alloys thereof, silicon, glass, carbon,ceramics, plastic, resins, and composites thereof, as well as suchmaterials having on the surface thereof a nonmagnetic film of adifferent material executed by means of a surface coating treatmentemploying a sputtering method, a vapor deposition method, a platingmethod, or the like. In particular, in the present invention, thesubstrate body may be either electrically conducting or insulating,since good magnetic characteristics may be obtained without theapplication of an electrical bias to the substrate body.

The nonmagnetic film provided on the surface of the substrate bodydescribed above should not magnetize at high temperatures, should beconductive, and should be easily mechanically worked and the like, butshould also have an appropriate degree of surface hardness. An exampleof a nonmagnetic layer meeting these conditions is (Ni--P) film producedby means of, for example, a sputtering method, or a plating method,which is preferentially employed.

With respect to the shape of the substrate, in the case of use as adisc, a circular doughnut shaped plate may be employed. The substratebody provided with a magnetic layer and the like described hereinbelow,that is to say, the magnetic recording medium, is employed whilerotating about an axis at the center of the plate at a speed of, forexample, 3600 rpm, during magnetic recording and reproduction. At thistime, the magnetic head rides above the magnetic recording medium at aheight of approximately 0.1 micrometer. Accordingly, it is necessary toappropriately control the flatness of the surface, the parallelness ofthe front and back surfaces, deformation in the circumferencialdirection of the substrate body, and the surface roughness thereof.

Furthermore, when the substrate body is rotated or stopped, the magneticrecording medium and the magnetic head come into contact and rub againsteach other at the surfaces thereof (contact start stop, termed CSS). Asa countermeasure, there are cases in which concentric light scratches(texturing) are provided in the surface of the substrate body.

Metallic Undercoat

Examples of the metallic undercoat in the present invention include, forexample, Cr, Ti, W, and alloys thereof. In the case in which an alloy isemployed, combinations with, for example, V, Nb, Ta, and the like, canbe proposed. In particular, Cr is preferable since it causes asegregation effect with respect to the ferromagnetic metal layerdescribed hereinbelow. Furthermore, it is widely used in massproduction, and the sputtering method, the vapor deposition method, orthe like may be employed as the formation method thereof.

With respect to the role of the metallic undercoating, this serves topromote crystal growth of the ferromagnetic metal layer when aferromagnetic metal layer comprising Co as a substrate body is providedthereon, so that the magnetization easy axis of the ferromagnetic metallayer will lie within the plane of the substrate body, in other words,so that the coercive force in a direction within the plane of thesubstrate body will be high.

When a metallic undercoat comprising Cr is formed by means of asputtering method, examples of film formation elements which control thecrystalline state thereof include, for example, the surface form of thesubstrate body, the surface state, or the surface temperature, the gaspressure during formation, a bias applied to the substrate body, and thethickness of the film formed, and the like. In particular, there is atendency for the coercive force of the ferromagnetic metal layer toincrease in proportion to the thickness of the Cr film, so thatconventionally, the Cr film thickness was within a range of 50 nm-150nm.

However, when the thickness of the Cr film described above is great,there is a tendency for the surface roughness of the medium to increase,and it is thus difficult to reduce the float distance of the magnetichead from the surface of the medium, and this interferes with a furtherincrease in recording density. In order to solve this problem, in thepresent invention, a ferromagnetic metal layer described hereinbelow isprovided on an ultrathin Cr film (for example, 2.5 nm), and a highcoercive force is realized thereby, so that it is possible to realizesuperior magnetic characteristics simultaneously with a stable reductionin the float height of the head.

Here, what is meant by conventional film formation conditions (filmformation conditions of the present invention) is conditions in whichthe background pressure of the film formation chamber is 10⁻⁷ (10⁻⁹)Torr, and the impurity concentration of the Ar gas employed during filmformation is 1 ppm or more (100 ppt or less, and preferably 10 ppb orless). Furthermore, the target employed during the formation of themetallic undercoat should preferably have an impurity concentration of150 ppm or less.

Furthermore, when the metallic undercoat is formed while applying a biasto the substrate body, the surface roughness of the metallic undercoatbecomes large, and as a result of the effects thereof, the surfaceroughness of the medium also becomes large. Accordingly, it ispreferable that a bias either not be applied, or be reduced to theminimum possible value, during the formation of the metallic undercoat.

Ferromagnetic Metal Layer

The ferromagnetic metal layer in accordance with the present inventionis appropriately employed in cases in which it is provided on thesurface of the substrate body via the metallic undercoat described above(that is to say, in the case of a metallic layer for recording withinthe surface); examples thereof include, for example, CoNiCr, CoCrTa,CoCrPt, CoNiPt, CoNiCrTa, CoCrPtTa, and the like. Among these, CoCrTa,which is widely produced as a low noise medium, and which is a materialsystem having an intergranular layer having a noncrystalline (amorphous)structure between crystalline particles, is optimal.

In particular, in the film formation conditions of the presentinvention, which involve an ultraclean atmosphere in comparison to theconventional film formation conditions, when the CoCrTa film comprises15-23 atm % chromium (Cr), 2-8 atm % tantalum (Ta), and a balance ofcobalt (Co), even if an electrical bias is not applied to the substratebody, a high coercive force of 2000 Oe or more can be obtained, and amagnetic recording medium having a small surface roughness may beformed. Furthermore, the same trends were confirmed in the case ofCoNiCrTa, and CoCrPtTa as well.

Here, what is meant by conventional film formation conditions (filmformation conditions of the present invention) are conditions in whichthe background pressure of the film formation chamber is 10⁻⁷ (10⁻⁹)Torr, and the impurity concentration of the Ar gas used during filmformation is 1 ppm or more (100 ppt or less, and preferably 10 ppb orless). Furthermore, the target employed during the formation of theferromagnetic metal layer should have an impurity concentration of 30ppm or less.

Magnetic Recording Medium Employing Magnetic Inversion

Examples of the "magnetic recording medium employing magnetic inversion"of the present invention include media in which recording magnetizationis formed parallel to the surface of the ferromagnetic metal layerdescribed above (in-plane magnetic recording medium). In this type ofmedium, in order to improve the recording density, it is necessary toachieve a further reduction in size of the recording magnetization.Since this reduction in size reduces the recording magnetization leakageflux, this reduces the reproduction signal output at the magnetic head.Accordingly, it is hoped that the medium noise, which is thought toresult from the effects of adjacent recording magnetization, will befurther reduced .

Oxygen Concentration in the Ferromagnetic Metal Layer

In the present invention, the "oxygen concentration in the ferromagneticmetal layer" is optimally 10 wt.ppm or less. It is disclosed ininternational application PCT/JP94/01184 that by means of limiting theoxygen concentration in this way, the coercive force of the medium isincreased, and the medium noise is reduced. What is meant by thesputtering method used for forming the ferromagnetic metal layer havingsuch an oxygen concentration is film formation under the followingconditions: the attained degree of vacuum in the film formation chamberused for forming the ferromagnetic metal layer is on the level of 10⁻⁹Torr, and the impurity concentration in the Ar gas used during theformation of the ferromagnetic metal layer is 100 ppt or less, andoptimally 10 ppb or less.

On the other hand, this concentration is known to be 250 wt.ppm or morein the case of CoCrTa films formed by means of conventional sputteringmethods. Here, what is meant by conventional sputtering methods is filmformation under the following conditions: the attained degree of vacuumin the film formation chamber used for the formation of theferromagnetic metal layer is on the level of 10⁻⁷ Torr, and the impurityconcentration of the Ar gas used during the formation of theferromagnetic metal layer is 1 ppm or more.

Oxygen Concentration in the Metallic Undercoat

In the present invention, the "oxygen concentration in the metallicundercoat" is optimally 100 wt.ppm or less. By means of limiting theoxygen concentration in this manner, it is possible to conduct crystalgrowth such that, even in cases in which the metallic undercoatcomprises an ultrathin film (for example, a Cr film of 2.5 nm), themagnetization easy access of the ferromagnetic metal layer formedthereon lies within the plane. As a result, it is possible to ensurethat the magnetic recording medium has sufficient magneticcharacteristics, and simultaneously to limit the size of the surfaceroughness of the metallic undercoat. The fact that in accordance withthis, the surface roughness of the magnetic recording medium is alsoreduced, and a low float height of the head becomes possible, isrecorded in international application PCT/JP94/01184. What is meant by asputtering method for formation of a metallic undercoat having such anoxygen concentration is film formation under conditions such that: theattained degree of vacuum in the film formation chamber used forformation of the metallic undercoat is on the level of 10⁻⁹ Torr, andthe impurity concentration in the Ar gas used during the formation ofthe metallic undercoat is 100 ppt or less, and optimally 10 ppb or less.

On the other hand, it is known that this concentration is 250 wt.ppm ormore in the case of Cr film produced by means of a conventionalsputtering method. Here, what is meant by a conventional sputteringmethod is film formation under conditions such that: the attained degreeof vacuum in the film formation chamber during the formation of the Crfilm is on the level of 10⁻⁷ Torr and the impurity concentration of Argas used during formation of the Cr film is 1 ppm or more.

Coercive Force Hc of the Magnetic Recording Medium

What is meant by the coercive force Hc of the magnetic recording mediumin the present invention is the resistance magnetic force of the mediumdetermined from the magnetization curves measured using a vibratingsample magnetometer (termed a VSM). The coercive force Hc is a valuemeasured within the plane of the thin film.

Aluminum Alloy

Examples of the aluminum alloy in the present invention include alloyscomprising, for example, aluminum and magnesium. Currently, in hard diskapplications, those using aluminum alloy as a substrate body are mostcommonly employed. Since the object of use is a magnetic recording use,it is preferable that the amount of metal oxides contained be small.

Furthermore, there are a number of cases in which a nonmagnetic (Ni--P)layer is provided by means of a plating method or sputtering method onthe surface of the aluminum alloy. The purpose of doing this is toincrease the corrosion resistance and the surface hardness of thesubstrate body. In order to reduce the abrasion force resulting when themagnetic head rubs against the surface of the medium, light concentricscratches (texturing) are provided in the surface of the (Ni--P) layer.

In particular, the use of a substrate body comprising an aluminum alloyhaving an average center line roughness Ra of 1 nm or less is preferablein order to reduce the surface roughness of the thin film formedthereon.

Glass

Examples of glass employed in the present invention include glass whichhas been subjected to strengthening treatment in which ion doping or thelike of the glass surface has been conducted, and glass which itselfcomprises microcrystals. Both of these are ways to eliminate the weakpoint of glass, that it is "easily breakable."

Since glass has a surface hardness which is higher than that of aluminumalloy, it is not necessary to provide a (Ni--P) layer or the like, sothat glass is superior in this respect. Furthermore, glass is alsoadvantageous from the point of view of forming the substrate body as athin plate, from the point of view of the smoothness of the substratebody surface, and from the point of view of the resistance of thesubstrate body to high temperatures.

In particular, in the present invention, even if an electrical bias isnot applied to the substrate body, it is possible to obtain superiormagnetic characteristics, so that it is possible to advantageouslyemploy a substrate body comprising glass, which is commonly aninsulating material. However, in order to produce a magnetic layerhaving a high coercive force, there are cases in which a nonmagneticlayer may be provided on the surface of the glass for the purpose ofincreasing the surface temperature of the substrate body during filmformation. Furthermore, there are cases in which a nonmagnetic layer isprovided in order to prevent the entry of harmful elements from theglass into the magnetic film. Alternatively, in order to reduce thefriction force resulting from the rubbing of the magnetic head againstthe surface of the medium, there are cases in which a nonmagnetic layerhaving an extremely fine undulating shape is provided on the surface ofthe glass.

Silicon

Examples of the silicon employed in the present invention include, forexample, silicon wafers formed into a disk shape, which are used in thesemiconductor field.

In the same way as glass, silicon has a high surface hardness, and it ispossible to form the substrate body into a thin plate shape, thesmoothness of the substrate body surface is also high, and theresistance to high temperatures of the substrate body is good, so thatin these respects it is superior to an aluminum alloy. In addition, itis possible to select the crystal orientation and the lattice constantof the substrate body surface, so that it is to be expected that theability to control the crystal growth of the magnetic layer formed onthis substrate body will improve. Furthermore, in the same manner as thealuminum alloy, the substrate body is conductive, so that it is possibleto apply a bias to the substrate body, and since the release of gasessuch H₂ O and the like from within the substrate body is slight, it ispossible to achieve an increase in cleanliness of the film formationspace, and this is advantageous.

Sputtering Method

Examples of the sputtering method employed in the present inventioninclude, for example, conveyance type sputtering methods in which thethin film is formed while moving the substrate body in front of thetarget, and static type sputtering methods in which the substrate bodyis fixed in front of the target and the thin film is formed. The formeris advantageous in the production of low cost media, since it issuitable for mass production, while the latter is capable of producingmedia having superior recording and playback characteristics, since theangle of incidence of the sputtering particles with respect to substratebody is stable. The latter method was employed in the embodiments of thepresent invention; however, the former method may also be employed.

Order of Formation of the Metallic Undercoat and the Ferromagnetic MetalLayer

In the present invention, what is meant by the "order of formation ofthe metallic undercoat and the ferromagnetic metal layer" is that "afterthe metallic undercoat has been formed on the surface of the substratebody, and until the ferromagnetic metal layer is formed on the surfacethereof, there is no exposure to an atmosphere having a higher pressurethan the gas pressure during film formation." After the surface of themetallic undercoat has been exposed to the ambient atmosphere, if aferromagnetic metal layer is formed thereon, the coercive force of themedium is known to decline dramatically (for example, from a level of1500 Oe with no exposure to a level of 500 Oe when there is exposure).

Impurities, and the Concentration Thereof, Present in the Ar Gas Used inFilm Formation

Examples of the "impurities present in the Ar gas used in filmformation" in the present invention include, for example, H₂ O, O₂, CO₂,H₂, N₂, C_(x) H_(y), H, C, O, CO and the like. In particular, impuritieswhich are thought to effect the amount of oxygen incorporated into thefilm are H₂ O, O₂, CO₂, O, and CO. Accordingly, the impurityconcentration in the present invention is expressed as the sum of the H₂O, O₂, CO₂, O, and CO contained in the Ar gas used in film formation.

Cleaning Treatment By Means of a High Frequency Sputtering Method

Examples of "cleaning treatment by means of a high frequency sputteringmethod" in the present invention include, for example, a method in whichAC voltage from a RF (radio frequency, 13.56 MHz) source is applied to asubstrate body positioned within a space having a gas pressurepermitting discharge. The characteristic feature of such a method isthat it may be applied even in cases in which the substrate body isnonconductive. Commonly, the effects of cleaning treatment include anincrease in the adhesion of the thin film to the substrate body.However, there are many unclear points with respect to the effectsexerted after cleaning treatment on the quality of the thin film itselfwhich is formed on the surface of a substrate body.

Impurities, and the Concentration Thereof, in the Cr Target which isEmployed During the Formation of the Metallic Undercoat

In the present invention, examples of the "impurities in the Cr targetemployed during the formation of the metallic undercoat" include, forexample, Fe, Si, Al, C, O, N, H, and the like. In particular, theimpurity which is assumed to have an influence on the amount of oxygenincorporated into the film is O. Accordingly, the impurity concentrationin the present invention is shown as the oxygen contained in the Crtarget used during formation of the metallic undercoat.

Impurities, and Concentrations Thereof, in the Target Used During theFormation of the Ferromagnetic Metal Layer

In the present invention, examples of the "impurities in the Co targetused during the formation of the ferromagnetic metal layer" include, forexample, Fe, Si, Al, Co, O, N, and the like. In particular, the impuritythought to affect the amount of oxygen incorporated in the film is O.Accordingly, the impurity concentration in the present invention isshown as the oxygen contained in the target used during formation of theferromagnetic metal layer.

Negative Bias Applied to the Substrate Body

In the present invention, the "negative bias applied to the substratebody" indicates the application of a DC bias voltage to the substratebody during the formation of a Cr undercoat or a magnetic layer as amagnetic recording medium. In the conventional sputtering methodsdescribed above, it is known that if the appropriate bias voltage isapplied, the coercive force of the medium can be increased. It iscommonly known that the effect of this bias application is greater inthe case in which such a bias is applied during the formation of bothlayers than in the case in which it is applied solely during theproduction of one or the other of the layers.

However, there are a number of cases in which the bias applicationdescribed above acts on substances in the vicinity of the substratebody, that is to say, on the substrate body support member or thesubstrate body holder. As a result, gas or dust is generated in thespace in the vicinity of the substrate body, and may be incorporatedinto the thin film during film formation, and a defective state islikely to be produced in which various film characteristics becomeunstable. Furthermore, the application of a bias to the substrate bodyhas the following problems.

(1) Such a bias can not be applied to nonconductive substrate bodiessuch as glass and the like.

(2) The saturation flux density (Ms) of the magnetic film which isformed declines.

(3) It is necessary to provide complicated machinery within the filmformation chamber.

(4) Changes occur easily in the degree of bias application to thesubstrate body, and as a result, undesirable variation is likely to begenerated in the magnetic characteristics.

As a countermeasure, it is possible to eliminate the problems describedabove by using CoCrTa having the composition described in the presentinvention as the ferromagnetic metal layer. Accordingly, it is possibleto obtain a magnetic recording medium which is capable of achieving ahigher recording density.

Attained Degree of Vacuum in the Film Formation Chamber Used for Formingthe Metallic Undercoat and/or Ferromagnetic Metal Layer

In the present invention the "attained degree of vacuum in the filmformation chamber used for forming the metallic undercoat and/orferromagnetic metal layer" is one film formation element controlling thevalue of the coercive force in accordance with the material of theferromagnetic metal layer. In particular, it is disclosed ininternational application PCT/JP94/01184 that conventionally, in Cobased materials containing Ta within the ferromagnetic metal layer, incases in which the attained degree of vacuum is low (for example, 5×10⁻⁶Torr or more), the effect thereof is large.

(Surface Temperature of the Substrate Body During Formation of theMetallic Undercoating and/or Ferromagnetic Metal Layer

In the present invention, the "surface temperature of the substrate bodyduring formation of the metallic undercoating and/or ferromagnetic metallayer" is one film formation element governing the value of the coerciveforce which does not depend on the material used for the ferromagneticmetal layer. It is possible to achieve a higher coercive force when filmformation is conducted at higher surface temperatures, insofar as thetemperature remains within a range which does not damage the substratebody. What is meant by damaging the substrate body is external changessuch as swelling, cracking, or the like, or internal changes such as ageneration of magnetization, an increase in the amount of gas released,or the like.

However, in order to realize a high substrate body surface temperature,it is commonly necessary to conduct some type of heating treatment,either in the film formation chamber or in a prechamber. This heatingtreatment has undesirable aspects in that gas or dust may be generatedin the space in the vicinity of the substrate body, and this may beincorporated into the thin film during film formation, and this may leadto instabilities in various film characteristics.

Furthermore, the high substrate body surface temperature involves thefollowing problems.

(1) The nonmagnetic NiP layer in a NiP/Al substrate body may bemagnetized.

(2) Warping is generated in the substrate body.

(3) In substrate bodies having low heat conductivity such as glass andthe like, it is difficult to raise the temperature of the substrate bodyand to maintain such a temperature.

Accordingly, a production method which makes it possible to obtain thedesired film characteristics either without conducting such heattreatment, or by conducting comparatively low-temperature heattreatment, has been desired.

Surface Roughness Ra of the Substrate Body

Examples of the surface roughness of the substrate body in the presentinvention include the average center line roughness Ra in the case inwhich the surface of a substrate body having a disk shape is measured inthe radial direction. The TALYSTEP produced by Rank Taylor HobsonCorporation was used as the measuring instrument.

When the substrate body begins to rotate from a stopped state, or in theopposite case, the surfaces of the magnetic recording medium and themagnetic head come into contact and rub against one another (contactstart stop, termed CSS). At this time, in order to suppress an increasein the adhesion of the magnetic head or the coefficient of friction, itis preferable that Ra be larger. On the other hand, when the substratebody has reached maximum rotation, it is necessary to maintain a spacebetween the magnetic recording medium and the magnetic head, in otherwords, it is necessary to guarantee the float height of the magnetichead, so that a low value of Ra is desirable.

Accordingly, the maximum and minimum values of the surface roughness Raof the substrate body are appropriately determined from the use and therequired specifications relating to the magnetic recording medium. Forexample, when the float height of the magnetic head is two microinches,Ra should be within a range of 6 nm-8 nm.

However, in order to achieve a further increase in recording density, itis necessary to further reduce the float height of the magnetic head(the distance by which the magnetic head is separated from the surfaceof the magnetic recording medium during the recording and playbackoperations). In order to achieve this, it is important to furtherflatten the surface of the magnetic recording medium. For this reason,it is desirable to further reduce the surface roughness of the substratebody.

In the present invention, conditions were considered under whichsuperior magnetic characteristics could be obtained even when asubstrate body having a Ra value of 0.5 nm was employed.

Texturing Treatment

Examples of the texturing treatment in the present invention include,for example, methods employing mechanical polishing, methods employingchemical etching, and methods providing a physically undulating film. Inparticular, when an aluminum alloy substrate body, which is the mostwidely employed type of substrate body, is used as the substrate body ofthe magnetic recording medium, the method employing mechanical polishingis adopted. For example, by applying a tape, having deposited on thesurface thereon an abrasive grain for grinding, to a (Ni--P) filmprovided on the surface of an aluminum alloy substrate body while thesubstrate body is rotating, concentric light scratches are produced. Inthis method, there are cases in which the abrasive grain used forgrinding is employed in a manner in which it is separated from the tape.

However, for the reasons described under the heading "Surface Roughnessof the Substrate body" above, a production method is desirable whichmakes it possible to obtain a variety of desired film characteristicseven without conducting the texturing treatment described above or in amore lightly textured state.

Composite Electropolishing Treatment

Examples of a composite electropolishing treatment of the presentinvention include, for example, treatment in which an oxide passivatedfilm having chromium oxides as a component thereof is provided on theinner walls of the vacuum chamber used for formation of the magneticfilm and the like. In this case, it is desirable that the material usedfor the inner walls of the vacuum chamber comprise, for example, SUS316Lor the like. By means of this treatment, it is possible to reduce theamount of O₂ and H₂ O emitted from the inner walls of the vacuumchamber, so that it is possible to further reduce the amount of oxygenincorporated into the thin film produced.

The magnetron sputtering apparatus produced by Anerba (number ILC3013:load lock static opposed type) used in the present invention has theabove treatment conducted on the inner walls of all of the vacuumchambers thereof (the loading/extraction chamber, the film formationchambers, and the cleaning chamber).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between the coercive force Hcand the saturation magnetization Ms, and the Cr concentration in theCoCrTa film, of a magnetic recording medium in accordance with a firstembodiment of the present invention.

FIG. 2 is a graph showing the relationship between the coercive force Hcand the saturation magnetization Ms, and the Ta concentration in theCoCrTa film, of a magnetic recording medium in accordance with thesecond embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the surface roughnessRa of a magnetic recording medium in accordance with a third embodimentof the present invention and the direct current bias applied to thesubstrate body.

FIG. 4 is a graph showing the relationship between the average diameterof the crystalline particles comprising the ferromagnetic metal layer ofa magnetic recording medium in accordance with the third embodiment ofthe present invention, and the direct current bias applied to thesubstrate body.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be explained in detail usingembodiments; however, the present invention is in no way restricted tothe embodiments described.

Embodiment 1

In the present embodiment, a ferromagnetic metal layer comprising(Co_(96-x) Cr_(x) Ta₄) [atm %] was laminated on a substrate bodycomprising an Al--Mg alloy plate having a NiP plating executed thereon,via a metallic undercoating comprising a Cr film, by means of asputtering method, and thereby a magnetic recording medium was produced.

The Cr concentration x in the ferromagnetic metal layer was alteredwithin a range of 10-24 [atm %].

Furthermore, in order to conduct a comparison with conventional filmformation conditions, the attained degree of vacuum within the filmformation chamber in which the ferromagnetic metal layer was formed wasaltered. The attained degree of vacuum within the film formation chamberused for forming the ferromagnetic metal layer was set to two values:approximately 10⁻⁹ Torr and approximately 10⁻⁷ Torr.

Furthermore, the DC bias applied to the substrate body during filmformation of the Cr and the CoCrTa had two values: 0 and 200 (-Volt).

At this time, the impurity concentration contained in the Ar gas duringformation of the ferromagnetic metal layer and the metallic undercoatwas set at 10 ppb.

In the present embodiment, the sputtering apparatus used in productionof the media was a magnetron sputtering device produced by Anerba(number ILC3013: load lock static opposed type), and the inner walls ofall the vacuum chambers thereof (the load/extraction chamber (andcleaning chamber), film formation chamber 1 (in which the metallicundercoat was formed), film formation chamber 2 (in which theferromagnetic metal layer was formed), and film formation chamber 3 (inwhich the protective layer was formed)), were subjected to compositeelectropolishing treatment. Table 1 shows the film formation conditionsduring production of the magnetic recording medium of the presentembodiment.

                  TABLE 1                                                         ______________________________________                                        Item                Set Values                                                ______________________________________                                        1) Substrate body material                                                                        Al--Mg alloy (having thereon a                                                10-micron (Ni--P) plated film)                            2) Diameter and shape of the                                                                      89 mm, disc-shaped                                        substrate body      No texturing, Ra <1 nm                                    3) Surface form of the                                                        substrate body                                                                4) Attained vacuum degree                                                                         10.sup.-7 or 10.sup.-9 (film formation                    (Torr)              chamber 2)                                                                    5 × 10.sup.-9 (except in film                                           formation chamber 2)                                      5) Impurity concentration in                                                                      10 ppb (same in all chambers)                             the Ar gas          2 (same in all chambers)                                  6) Ar gas pressure (mTorr)                                                                        250 (same in all chambers)                                7) Temperature (° C.) at which                                         the substrate body surface is                                                 maintained                                                                    8) Target material (at %)                                                                         Cr, Co.sub.96-x Cr.sub.x Ta.sub.4, C                      9) Diameter of the target                                                                         6                                                         (inches)            120 (Cr), 20 (CoCrTa)                                     10) Impurity concentration in                                                                     35 (Cr, CoCrTa, C)                                        the target (ppm)    DC, 200 (Cr, CoCrTa)                                      11) Distance between target                                                                       DC, 400 (C)                                               and substrate bddy (min)                                                                          0 or 200 (Cr, CoCrTa)                                     12) Power (W) applied to the                                                                      0 (C)                                                     target              2.5 (Cr), 16-28 (CoCrTa), 10                              13) DC bias (-Volt) applied                                                                       (C)                                                       to the substrate body during                                                  film formation                                                                14) Film thickness produced                                                   (nm)                                                                          Substrate body cleaning                                                       treatment conditions                                                          15) Power (W) applied to the                                                                      200                                                       substrate body                                                                16) Treatment time (sec)                                                                          10                                                        17) Ar gas pressure (mTorr)                                                                       2                                                         ______________________________________                                    

Hereinbelow, the production method of the magnetic recording medium ofthe present invention will be explained in order of the processesthereof. The numbers in parentheses below indicate this order.

(1) An aluminum alloy plate having a disc shape such that the inner andouter diameters were 25 mm/89 mm, and the thickness thereof was 1.27 mm,was employed as the substrate body. An (Ni--P) film having a thicknessof 10 microns was provided on the surface of this aluminum alloy plateby means of a plating method. The surface of the (Ni--P) film was workedusing a mechanical method so as to attain a flat state without providingconcentric light scratches (texturing), and the surface roughness of thesubstrate body when scanned in the radial direction of the disk was suchthat the average centerline roughness Ra was less than 1 nm.

(2) The substrate body described above was subjected to a washingtreatment using mechanical and chemical methods, and to a dryingtreatment using hot air or the like, prior to the subsequent filmformation.

(3) After the drying treatment had been completed, the substrate bodywas set in a substrate body holder comprising aluminum which wasdisposed in the load chamber of the sputtering apparatus. The interiorof the load chamber was evacuated using a vacuum exhaust device to anattained degree of vacuum of 3×10⁻⁹ Torr, and then, the substrate bodywas subjected to a heating treatment for a period of 5 minutes and at atemperature of 250° C. using an infrared lamp.

(4) The substrate body holder described above was moved from a loadchamber to a cleaning chamber. After being moved, the substrate body wasmaintained at a temperature of 250° C. using an infrared lamp.

(5) Ar gas having an impurity concentration of 10 ppb was introducedinto the cleaning treatment chamber, and the gas pressure was set to 2mTorr.

(6) A voltage was applied from a RF power source to the substrate bodydescribed above, and a cleaning treatment was conducted. The conditionsthereof were as follows: the power applied to the substrate body was 200W (a power density of 2.5 W/cm², and a cleaning speed of 0.013 nm/sec),and the cleaning treatment time was fixed at 10 seconds.

(7) The substrate body holder described above was then moved from thecleaning treatment chamber to a film formation chamber 1 used forproduction of the Cr film. After being moved, the substrate body wasmaintained at a temperature of 250° C. using an infrared lamp. However,film formation chamber 1 was evacuated in advance to an attained degreeof vacuum of 3×10⁻⁹ Torr, and after the substrate body holder had beenmoved, a door valve between the cleaning treatment chamber and the filmformation chamber 1 was closed. The impurity concentration in the Crtarget used was 120 ppm.

(8) Ar gas was introduced into film formation chamber 1, and the gaspressure of film formation chamber 1 was set to 2 mTorr. The impurityconcentration of the Ar gas used was set at 10 ppb.

(9) A voltage of 200 W was applied from a direct current power source tothe Cr target, and a plasma was generated. As a result, the Cr targetwas caused to sputter, and a Cr layer having a thickness of 2.5 nm wasformed on the surface of the substrate body, which was positionedparallel to and opposite from the target.

(10) After the formation of the Cr layer, the substrate body holder wasmoved from the film formation chamber 1 to a film formation chamber 2,used for the production of a CoCrTa film. After being moved, thesubstrate body was maintained at a temperature of 250° C. using aninferred lamp. However, the conditions were varied with respect to theattained degree of vacuum of film formation chamber 2 prior toformation. Two conditions were used: a case in which evacuation wasconducted to a level of 3×10⁻⁹ Torr, and a case in which evacuation wasconducted to a level of 1×10⁻⁷ Torr. Furthermore, after the substratebody holder had been moved, a door valve between film formation chamber1 and film formation chamber 2 was closed. The composition of the targetemployed was set to (Co_(96-x) Cr_(x) Ta₄) where x varied within a rangeof 10-24 (atm %), and the impurity concentration in the target was setto 20 ppm.

(11) Ar gas was introduced into film formation chamber 2, and the gaspressure within film formation chamber 2 was set to 2 mTorr. Theimpurity concentration in the Ar gas employed was set to 10 ppb.

(12) A voltage of 200 W was applied from a direct current power sourceto a CoCrTa target, and a plasma was generated. As a result, the CoCrTatarget was caused to sputter, and CoCrTa layers having thicknesseswithin a range of 16-28 nm were formed on the surface of the substratebody provided with a Cr layer, which was parallel and in opposition tothe target.

(13) After formation of the CoCrTa layer, the substrate body holder wasmoved from film formation chamber 2 to a film formation chamber 3, whichwas used for production of a C film. Even after being moved, thesubstrate body was maintained at a temperature of 250° C. using aninferred lamp. However, film formation chamber 3 was evacuated to anattained vacuum degree of 3×10⁻⁹ Torr in advance, and after moving thesubstrate body holder, a door valve between film formation chamber 2 andfilm formation chamber 3 was closed.

(14) Ar gas was introduced into film formation chamber 3, and the gaspressure within film formation chamber 3 was set to 2 mTorr. Theimpurity concentration in the Ar gas employed was set to 10 ppb.

(15) A voltage of 400 W was applied from a direct current power sourceto a C target, and a plasma was generated. As a result, the C target wascaused to sputter, and a C layer having a thickness of 10 nm was formedon the surface of the substrate body, which was provided with a CoCrTalayer and a Cr layer, and which was positioned parallel and inopposition to the target.

(16) After the formation of the C layer, the substrate body holder wasmoved from the film formation chamber 3 to an extraction chamber. Afterthis, N₂ gas was introduced into the extraction chamber, atmosphericpressure was established, and then the substrate body was removed. Bymeans of procedures (1)-(12) above, a magnetic recording medium havingthe layered structure of C/CoCrTa/Cr/NiP/Al was formed.

The targets employed had extremely restricted impurity levels. Theimpurities present in the target use for Cr formation were as follows:Fe: 88, Si: 34, Al: 10, C: 60, O: 120, N: 60, H: 1.1 (wt.ppm).Furthermore, the composition of the target used for the formation of theferromagnetic metal layer was such that Cr: 10-24 at %, Ta: 4 at %, andCo comprised the balance, while the impurities therein were such thatFe: 27, Si<10, Al<10, C: 30, O: 20, and N>10 (wt.ppm).

In FIG. 1, the magnetic characteristics of the media produced are shown.The horizontal axis in FIG. 1 indicates the Cr concentration of theCoCrTa film. The measurement of this Cr concentration was conducted bymeans of SIMS. The vertical axis in FIG. 1 indicates the saturationmagnetization Ms (emu/cc) and the coercive force Hc (Oe) in thecircumferencial direction of the sample. In FIG. 1, the meaning of the ◯symbol, the  symbol, and the × symbol are as given in Table 2 below.

                  TABLE 2                                                         ______________________________________                                                   Attained Vacuum                                                               Degree (Torr) in                                                                          Bias [-V] During                                                  Film Formation                                                                            Formation of the Cr                                    Symbol     Chamber 2   and CoCrTa Films                                       ______________________________________                                        ◯                                                                            3 × 10.sup.-9                                                                       0                                                                                                                                 3 × 10.sup.-9                                                                       200                                                    X          1 × 10.sup.-7                                                                       0                                                      ______________________________________                                    

The following three points are clear from FIG. 1.

(1) In the case in which the atmosphere was ultraclean and a bias wasnot applied (◯ symbol), when the Cr concentration in CoCrTa film (in atm%) was within a range of 14-23, a magnetic recording medium having acoercive force of 2000 Oe or more was obtained.

(2) When film formation was conducted in an ultraclean atmosphere (◯symbol), a coercive force was obtained which was dramatically higherthan that obtained by film formation in a conventional atmosphere (×symbol).

(3) When a bias was not applied (◯ symbol) the coercive force which wasobtained was higher than that obtained when a bias was applied (symbol).

Accordingly, in a magnetic recording medium employing reversal ofmagnetization which is provided with a ferromagnetic metal layercomprising CoCrTa having an oxygen content of 100 wt.ppm or less,provided on a substrate body via a metallic undercoat comprising Crhaving an oxygen concentration of 100 wt.ppm or less, by means ofsetting the composition of the ferromagnetic metal layer to chromium(Cr) within a range of 14-23 atm %, tantalum (Ta) at 4 atm %, thebalance comprising cobalt (Co), it is possible to obtain a magneticrecording medium having superior magnetic characteristics withoutapplying a bias to the substrate body.

Embodiment 2

In the present embodiment, a ferromagnetic metal layer comprising(Co_(83-y) Cr₁₇ Ta_(y)) [atm %] was laminated on a substrate bodycomprising a Al--Mg alloy plate having a NiP plating executed thereon,via a metallic undercoat comprising a Cr film, using a sputteringmethod, and a magnetic recording medium was thus obtained.

The Ta concentration y in the ferromagnetic metal layer was alteredwithin a range of 0-9 [atm %].

The other points were identical to those in Embodiment 1.

Table 3 shows the film formation conditions during production of themagnetic recording medium of the present embodiment; only thecomposition of the ferromagnetic metal layer differs from that ofEmbodiment 1. The production method for the magnetic recording medium ofthe present embodiment was identical to that of Embodiment 1.

                  TABLE 3                                                         ______________________________________                                        Item                Set Values                                                ______________________________________                                        1) Substrate body material                                                                        Al--Mg alloy (having thereon a                                                10-micron (Ni--P) plated film)                            2) Diameter and shape of the                                                                      89 mm, disc-shaped                                        substrate body                                                                3) Surface form of the                                                                            No texturing, Ra <1 nm                                    substrate body                                                                4) Attained vacuum degree                                                                         10.sup.-7 or 10.sup.-9 (film formation                    (Torr)              chamber 2)                                                                    5 × 10 .sup.-9 (except in film                                          formation chamber 2)                                      5) Impurity concentration in                                                                      10 ppb (same in all chambers)                             the Ar gas                                                                    6) Ar gas pressure (mTorr)                                                                        2 (same in all chambers)                                  7) Temperature (° C.) at which                                                             250 (same in all chambers)                                the substrate body surface is                                                 maintained                                                                    8) Target material (at %)                                                                         Cr, Co.sub.83-y Cr.sub.17 Ta.sub.y, C                     9) Diameter of the target                                                                         6                                                         (inches)                                                                      10) Impurity concentration in                                                                     120 (Cr), 20 (CoCrTa)                                     the target (ppm)                                                              11) Distance between target                                                                       35 (Cr, CoCrTa, C)                                        and substrate body (mm)                                                       11) Power (W) applied to the                                                                      DC, 200 (Cr, CoCrTa)                                      target              DC, 400 (C)                                               12) DC bias (-Volt) applied                                                                       0 or 200 (Cr, CoCrTa)                                     to the substrate body during                                                                      0 (C)                                                     film formation                                                                13) Film thickness produced                                                                       2.5 (Cr), 1.6-28 (CoCrTa), 10                             (nm)                (C)                                                       Substrate body cleaning                                                       treatment conditions                                                          14) Power (W) applied to the                                                                      200                                                       substrate body                                                                15) Treatment time (sec)                                                                          10                                                        16) Ar gas pressure (mTorr)                                                                       2                                                         ______________________________________                                    

FIG. 2 shows the magnetic characteristics of the media produced. Thehorizontal axis in FIG. 2 shows the Ta concentration in the CoCrTa film.The measurement of this Ta concentration was conducted using SIMS. Thevertical axis in FIG. 2 indicates the saturation magnetization Ms[emu/cc] and the coercive force Hc [Oe] in the circumferencial directionof the sample. In FIG. 2, the conditions indicated by the ⋄ symbol, the♦ symbol, and the + symbol are as shown in Table 4 below.

                  TABLE 4                                                         ______________________________________                                                   Attained Vacuum                                                               Degree (Torr) in                                                                          Bias [-V] During                                                  Film Formation                                                                            Formation of the Cr                                    Symbol     Chamber 2   and CoCrTa Films                                       ______________________________________                                        ⋄  3 × 10.sup.-9                                                                       0                                                      ♦                                                                          3 × 10.sup.-9                                                                       200                                                    +          1 × 10.sup.-7                                                                       0                                                      ______________________________________                                    

The following three points are clear from FIG. 2.

(4) When formation was conducted in an ultraclean atmosphere and withoutapplying a bias (⋄ symbol), when the Ta concentration y [in atm %] inthe CoCrTa film was within a range of 2-8, then it was possible toobtain a magnetic recording medium having a coercive force of 2000 Oe ormore.

(5) When film formation was conducted in an ultraclean atmosphere (⋄symbol), the coercive force obtained was dramatically higher than thatwhen film formation was conducted in a conventional atmosphere (+symbol).

(6) When a bias was not applied (⋄ symbol), the coercive force washigher than that obtained when a bias was applied (♦ symbol).

Accordingly, in magnetic recording media employing reversal ofmagnetization which are provided with a ferromagnetic metal layercomprising CoCrTa having an oxygen concentration of 100 wt.ppm or less,provided on a substrate body via a metallic undercoat comprising Crhaving an oxygen concentration of 100 wt.ppm or less, by means ofsetting the composition of the ferromagnetic metal layer to chromium(Cr) in an amount of 17 atm %, tantalum (Ta) in an amount within a rangeof 2-8 atm %, and the balance comprising cobalt (Co), then it ispossible to obtain a magnetic recording medium having superior magneticcharacteristics without applying a bias to the substrate body.

It was learned, from the results of the first and second embodimentsdescribed above, that in magnetic recording media employing reversal ofmagnetization, which are provided with a ferromagnetic metal layercomprising CoCrTa having an oxygen concentration of 100 wt.ppm or less,provided on a substrate body via a metallic undercoat comprising Crhaving an oxygen concentration of 100 wt.ppm or less, if the compositionof the ferromagnetic metal layer is set to chromium (Cr) in an amountwithin a range of 14-23 atm %, tantalum (Ta) in an amount within a rangeof 2-8 atm %, and the balance comprising cobalt (Co), then it ispossible to obtain a magnetic recording medium having superior magneticcharacteristics without applying a bias to the substrate body.

Embodiment 3

In the present embodiment, a metallic undercoat comprising a Cr film,and a ferromagnetic metal layer comprising (Co₇₉ Cr₁₇ Ta₄) [atm %] weredeposited in order using a sputtering method on a substrate bodycomprising a Al--Mg alloy plate having a NiP plating executed thereon,and when this was done, the value of the direct current bias applied tothe substrate body was varied, and magnetic recording media wereproduced.

The value E of the direct current bias was altered within a range of0-300 [-Volt]. Here, the attained degree of vacuum in the film formationchamber used for the formation of the ferromagnetic metal layer wasfixed at approximately 10⁻⁹ Torr.

The other points were identical to those of Embodiment 1.

Table 5 shows the film formation conditions during the production of themagnetic recording media of the present embodiment. The productionmethod of the magnetic recording media of the present embodiment isidentical to that of Embodiment 1.

                  TABLE 5                                                         ______________________________________                                        Item                Set Values                                                ______________________________________                                        1) Substrate body material                                                                        Al--Mg alloy (having thereon a                                                10-micron (Ni--P) plated film)                            2) Diameter and shape of the                                                                      89 mm, disc-shaped                                        substrate body                                                                3) Surface form of the                                                                            No texturing, Ra < 1 nm                                   substrate body                                                                4) Attained vacuum degree                                                                         5 × 10.sup.-9 (same in all chambers)                (Torr)                                                                        5) Impurity concentration in                                                                      19 ppb (same in all chambers)                             the Ar gas                                                                    6) Ar gas pressure (mTorr)                                                                        2 (same in all chambers)                                  7) Temperature (° C.) at which                                                             250 (same in all chambers)                                the substrate body surface is.                                                maintained                                                                    8) Target material (at %)                                                                         Cr, Co.sub.79 Cr.sub.17 Ta.sub.4, C                       9) Diameter of the target                                                                         6                                                         (inches)                                                                      10) Impurity concentration in                                                                     120 (Cr), 20 (CoCrTa)                                     the target (ppm)                                                              11) Distance between target                                                                       35 (Cr, CoCrTa, C)                                        and substrate body (mm)                                                       12) Power (W) applied to the                                                                      DC, 200 (Cr, CoCrTa)                                      target              DC, 400 (C)                                               13) DC bias (-Volt) applied                                                                       0-300 (Cr, CoCrTa)                                        to the substrate body,durinq                                                                      0 (C)                                                     film formation                                                                14) Film thickness produced                                                                       2.5 (Cr), 16-28 (CoCrTa), 10                              (nm)                (C)                                                       Substrate body cleaning                                                       treatment conditions                                                          15) Power (W) applied to the                                                                      200                                                       substrate body                                                                16) Treatment time (sec)                                                                          10                                                        17) Ar gas pressure (mTotr)                                                                       2                                                         ______________________________________                                    

In FIG. 3, the surface roughness Ra of the media produced is shown. Thehorizontal axis in FIG. 3 indicates the direct current bias E [-Volt]applied to the substrate body during the deposition of the metallicundercoat and the ferromagnetic metal layer. The vertical axis in FIG. 3indicates the surface roughness Ra [nm] of the sample.

It can be seen from FIG. 3 that the application of a smaller directcurrent bias E permits the formation of a medium having a smallersurface roughness, and when E is equal to 0, that is to say, when nobias is applied, the minimum value is obtained.

FIG. 4 shows the results of a measurement of the average particlediameter of the crystals comprising the ferromagnetic metal layer, froma TEM (transmission electron microscope) taken of the ferromagneticmetal layer of the media produced.

The TEM observation conditions are as shown in Table 6 below.

                  TABLE 6                                                         ______________________________________                                        <Sample production Method>                                                    ______________________________________                                        (1) Polishing was conducted with respect to the sample surface                on which film formation had not been conducted, and the sample                thickness was set to 10 microns.                                              (2) Next, ion milling was conducted from the surface of the                   sample on which film formation had not been conducted, and the                sample thickness was set to 5 nm or less. The chief                           conditions were: Ar ion doping, 4.5 kV × 5 mA, angle of                 incidence of 15 degrees.                                                      <TEM Observation Conditions>                                                  (1) TEM employed: Hitachi HF2000                                              (2) Acceleration voltage: 200 kV                                              <Particle Diameter Observation Conditions>                                    (1) Magnification of the TEM image employed: 850000×                    (2) Particle diameter measuring method: the outline of the                    crystalline particles was captured on an OHP sheet from the                   TEM image. This was scanned into a personal computer (a                       Macintosh LC 575). The average particle diameter was                          determined using image processing software ("NIH Image                        1.56b18" by Wayne Rasband, National Institutes of Health,                     USA).                                                                         ______________________________________                                    

It can be seen from FIG. 4 that in cases in which a small direct currentbias E is applied, the average particle diameter of the crystalscomprising the ferromagnetic metal layer becomes smaller, and when E hasa value of 0, that is to say, when no bias is applied, the smallestvalue is obtained.

Accordingly, it has been determined that by forming a magnetic recordingmedium having a ferromagnetic metal layer comprising a CoCrTa filmhaving a component ratio in accordance with the present inventionwithout applying a bias, not only are superior magnetic characteristicsobtained, but it is also possible to realize a reduction in the headfloat height and a reduction in the noise of the medium. Furthermore,since it is possible to conduct film formation without applying a bias,it is clear that in the case of magnetic recording media having aferromagnetic metal layer comprising a CoCrTa film having a componentratio in accordance with the present invention, it is possible toproduce such a magnetic recording medium having superior magneticcharacteristics not only when conductive substrate bodies comprisingsilicon and the like, which are desirable when attempts are made to makethe magnetic recording medium thinner, are employed, but also wheninsulating substrate bodies such as glass or ceramics or the like areemployed.

INDUSTRIAL APPLICABILITY

As described above, in accordance with the present invention, a magneticrecording medium having a low surface roughness and comprising arecording layer composed of magnetic particles having a small diameter,and having a high coercive force, and a manufacturing method for suchmedia, are obtained.

What is claimed is:
 1. A magnetic recording medium employing reversal ofmagnetization provided with a substrate body, a metallic undercoatcomprising Cr having an oxygen content of 100 wt.ppm or less, and aferromagnetic metal layer comprising CoCrTa having an oxygen content of100 wt.ppm or less, whereinthe composition of said ferromagnetic metallayer contains chromium (Cr) in an amount within a range of 14-23 atm %,tantalum (Ta) in an amount within a range of 2-8 atm %, the balancecomprising cobalt (Co).
 2. A magnetic recording medium in accordancewith claim 1, wherein the formation of said magnetic recording mediumbeing characterized by said substrate body remaining substantiallyelectrically unbiased at least during the formation of saidferromagnetic metal layer.
 3. A magnetic recording medium in accordancewith claim 1, wherein said substrate body has a disc shape, and whereinno concentric texturing treatment is provided on the surface of saidsubstrate body.
 4. A magnetic recording medium in accordance with claim3, wherein the surface roughness of said substrate body is such thatwhen roughness scanning is conducted in the radial direction of thedisk, the average center line roughness Ra is smaller than 1 nm.
 5. Amagnetic recording medium in accordance with claim 1, wherein saidsubstrate body comprises a conductive material.
 6. A magnetic recordingmedium in accordance with claim 1, wherein said substrate body comprisesan insulating material.
 7. A magnetic recording medium in accordancewith claim 5, wherein said conductive material comprises aluminum oralloy thereof.
 8. A magnetic recording medium in accordance with claim5, wherein said conductive material comprises titanium or an alloythereof.
 9. A magnetic recording medium in accordance with claim 5,wherein said conductive material comprises silicon.
 10. A magneticrecording medium in accordance with claim 6, wherein said insulatingmaterial comprises one of glass, carbon, ceramic, plastic, resin, or acomposite thereof.
 11. A magnetic recording medium in accordance withclaim 5, wherein a nonmagnetic layer is provided on said conductivematerial.
 12. A magnetic recording medium in accordance with claim 6,wherein a nonmagnetic layer is provided on said insulating material. 13.A magnetic recording medium in accordance with claim 11, wherein saidnonmagnetic layer comprises a (Ni--P) film produced by means of one of asputtering method and a plating method.
 14. A magnetic recording mediumin accordance with claim 12, wherein said nonmagnetic layer comprises a(Ni--P) film produced by means of one of a sputtering method and aplating method.